IMO from my own experience,
I have never found any of the filtered seawater sold/free to be consistent year round.
Yes, there are many of my service customers and installs that like the convenience of not mixing, but they usually have never ending nusance issues.algae ,diatoms,alk, smell etc..just check out the cleanliness of the water barrel at the store next time you buy some..
Yes, Iam aware of bad batches of synthetic mixes sold in the past.
its up to the user to QC as best we can.
I have visited several places (some in long beach area) and have seen the filtering process, not exactly the super duper cleaning i was expecting.
and watched them add a crap-load of buffer to "get it right" for use
there are many things that due to costs and time ,these companies just didnt do,but the water was clean enough for people to use and for the most part, most hobbyists have pretty good luck with filtered seawater
I also had a customer who worked for a municipal treatment center run some tests on various samples i gave him in his lab some years ago and he found crazy amounts of impurities, such as sulfer,lead, gasoline and petrolium by products ,that spooked me enough to stop .
when u do aquarium service for a living and you ask people to spend all kinds of money for rare or expensive livestock and good equipment, why chance it all to a questionable water source? just to save a few bucks? really?
when livestock dies, customers get upset
then they dont pay you, that is not good for business
all of these animals came from half way around the world and survived all sorts of hell to get here,just so you can put them in a clear box to watch them
why make them suffer existence in water that is not as pure as you can best provide?
all we can do is give them the best possible environment to thrive, not just survive.
right??